The present invention relates generally to the computer enhanced imaging. More particularly it relates to a method and apparatus for editing a full-color image so that input data relating to an original color image is processed in such a manner that an observer of the output image will perceive a desired correspondence of image parameters between the two images.
The actual or perceived quality of an imaging system depends to a large extent upon a degree to which the output image, whether printed or electronically displayed, appears to match the input image or subject. In the case of a color image reproduction system, such as a scanner, wherein an input color image is copied to produce an output color image, the match between input and output extends to the color content of the image as well as the achromatic subject information. Thus the various shades and intensities of the different colors must be properly matched. Ideally, the colors of the output image should be indistinguishable from those of the input image.
Alternatively, a user may choose to purposely alter color and sharpness from that of the original image in order to accentuate aspects of the image or for various other reasons.
In order to accommodate such image changes in image scanning systems a pre-scan is used to bring image data to a central processing unit, such as a personal computer connected to the scanner, wherein software is running which allows a user to adjust color and hue information of the image.
There are many commercially available scanning systems which use one dimensional video lookup tables to change a limited number of variables in the image to immediately show a user a simulated version of what the image will look like a final scan. By doing so, the software makes use of the actual video device's lookup tables without accessing the actual color data read in from the scanner. While this does save some time, it is a simulation and provides an extremely limited number of variables that may be changed and the color and hue representation of the simulation can and often is off by a significant amount. In either case a user generally wishes to have editing ability of a full color image.
A second problem arises in scanning systems which require a re-scan in order to accurately update an output image to reflect changes to color or sharpness dictated by a user. Not only is re-scanning time consuming to recapture an image and reprocess electronic data resulting from the scan, but also such a requirement stops the user from being able to take out the subject to do side-by-side comparisons. In the case of slides, it is often desirable to be able to place the slide on a light table next to a host computer so that results of the scan can be displayed on the computer and a direct comparison.
A further problem arises in scanners which perform processing and image adjustment calculations at the same byte length as will be transmitted to the host, or alternatively convert to a lower byte length prematurely. If a scanner processes image data in eight bit bytes, for example, the processed data will have a lower tonal resolution due to accumulation of calculation errors. This phenomenon is known as "contouring." To a lesser extent, this also occurs if processing is performed at ten bit bytes and is then converted to eight bits before certain processing occurs, color enhancement for example.
Therefore, it is an object of the invention to provide an editing system for full color images which provides accurate representation of colors and hues of the image.
It is another object of the invention to allow a user to remove the input image, such as a color slide, from the scanner for comparison purposes while performing image enhancement of an image of the subject.
It is a further object of the invention to increase tonal resolution of the output image and maintain data precision by performing substantially all processing at a byte length greater than required by the host.
These and other object of the inventions will become apparent and will appear hereinafter.